The present invention relates generally to agitation devices and dispensing systems incorporating such agitation devices, and, more particularly, to agitation devices and dispensing systems (for example, injection systems) for use in connection with delivery of a multi-component medium to a patient.
In a number of medical procedures, it is desirable to inject a multi-component injection medium into a patient. An example of such a medical procedure is ultrasound imaging.
Ultrasound imaging creates images of the inside of the human body by broadcasting ultrasonic energy into the body and analyzing the reflected ultrasound energy. Differences in reflected energy (for example, amplitude or frequency) appear as differences in gray scale or color on the output images. As with other medical imaging procedures, contrast enhancing fluids (often referred to as contrast media) can be injected into the body to increase the difference in the reflected energy and thereby increase the gray scale or color contrast displayed in the image (that is, the image contrast) viewed by the operator.
For ultrasonic imaging, the most common contrast media contain many small bubbles. The difference in density of bubbles when compared to water, and thus their difference in sound transmission, makes small gas bubbles excellent means for scattering ultrasound energy. Small solid particles can also serve to scatter ultrasonic energy. Such particles are typically on the order of 1 to 10 microns (that is, 10xe2x88x926 to 10xe2x88x925 meters) in diameter. These small particles can pass safely through the vascular bed.
Contrast media suitable for use in ultrasound are supplied in a number of forms. Some of these contrast media are powders to which liquid is added just before use. The powder particles cause a gas bubble to coalesce around them. The powder must be mixed with a liquid, and the mixture must be agitated with just the right amount of vigor to obtain the optimum creation of bubbles. Another type of contrast medium is a liquid that is agitated vigorously with air. There are no solid particles to act as nuclei, but the liquid is a mixture of several liquid components that make relatively stable small bubbles. A third type of contrast medium uses xe2x80x9chardxe2x80x9d spheres filled with a gas. These contrast media are typically supplied as a powder that is mixed with a liquid. The goal is to suspend the spheres in the liquid without breaking them. Even though such spheres have a shell that is hard compared to a liquid, they are very small and relatively fragile. It is also possible for the solid particles themselves to act to scatter ultrasonic energy, but the acoustical properties of the solid spheres are not as different from water as those of a gas so the difference in reflected energy is not as dramatic.
Contrast medium particles also enhance other modes of ultrasonic imaging. For example, when the particles are carried along in the blood stream, the reflected energy is Doppler shifted. This Doppler shift allows an estimation of the speed of blood flow. Bubbles can also be excited so that they radiate ultrasonic energy at the second harmonic of the incident ultrasonic energy. This harmonic imaging is dependent upon the non-linearity of the reflectors. Gas bubbles work well as harmonic reflectors.
After mixing/preparation as described above, the contrast medium is drawn into a syringe or other container for injection into the patient. Typically, the fluid is injected into the vein in the arm of the patient. The blood dilutes and carries the contrast medium throughout the body, including to the area (i.e., the region-of-interest or ROI) of the body being imaged.
It is becoming more common for a microprocessor controlled power injector to be used for injecting the contrast medium. Compared to a hand injection of contrast, this has the benefit of maintaining a consistent flow over a long time, thereby providing a consistent amount of contrast medium (number of particles) in the blood stream. If there are too few particles, for example, there is insufficient image contrast and the diagnosis cannot adequately be made. If too many particles are present, too much energy is reflected, resulting in blooming or saturation of the ultrasound receiver.
Although a power injector can inject contrast medium at a constant flow rate, there must be a constant number of bubbles per volume of fluid injected to provide a constant image contrast. Because a gas is significantly less dense than water and other liquids, however, gas bubbles will rise in a liquid. The rate of rise is related to the diameter of the gas bubble. This density difference provides a useful tool to quickly separate large bubbles created during the initial mixing. However, the small bubbles desired for image enhancement will also rise slowly. Solid particles, on the other hand, will tend to settle or sink because most solids are more dense than water. Many minutes can elapse between the initial mixing of the contrast medium and the injection into the patient, and/or the injection itself may be several minutes in duration. If the concentration of particles changes, the image contrast may be degraded.
It is, therefore, very desirable to develop systems and methods to maintain multi-component contrast media in a mixed state throughout an injection proceeding.
The present invention provides devices, systems and methods for dispensing a multi-component medium (for example, an ultrasound contrast medium) via injection into a patient. Such a system includes generally at least a first container to hold the medium, a pressurizing device, such as a pump, in fluid connection with the container for pressurizing the medium, and an agitation mechanism or device to maintain the components of the medium in a mixed state. The container and the pressurizing device can be separate units, as in the case of an bag or bottle in fluid connection with a peristaltic or other type of pump. The container and the pump can also be combined as a single unit, as in the case of a syringe, wherein the syringe barrel of the syringe acts to contain the medium and the syringe plunger pressurizes the medium within the syringe barrel.
The contrast media with which this invention operates optimally contain contrast enhancement agents which interact with the energy beamed into the body for creation of the image. The energy can be ultrasonic or electromagnetic. Common electromagnetic energies include X-rays and light. The contrast enhancement agents include but are not limited to microbubblesxe2x80x94with or without a solid core or nucleus, microspheres with relatively rigid shells filled with gas or liquid, liposomes with relatively flexible shells filled with gas or liquid, solid micro-particles, or microspheres of a liquid that is not miscible with the liquid in the contrast media. Any contrast media involving two immiscible materials or different phases of material could benefit from this invention. Contrast media where the molecules of the contrast enhancing material dissolve in the liquid of the contrast media can benefit from this invention to the extent that they are mixed from two different phases or to the extent that they might separate during storage or use.
In one embodiment, the agitation mechanism operates by inducing bulk motion of the first container. In this embodiment, free moving or fixed objects may be placed within the container to assist in mixing. The agitation mechanism may, for example, rotate or shake randomly the first container about a point.
The agitation mechanism may also rotate the first container about at least one axis of the container. In this embodiment, the first container may be formed asymmetrically about the axis to reduce the effects of rotational symmetry. The first container may also include a fixed or movable flow member therein to reduce the effects of rotational symmetry about the axis.
In another embodiment, the agitation mechanism induces currents within the medium without bulk motion of the container. For example, the agitation mechanism may include a movable stirring member within the first container. Moreover, convection currents may be induced in the medium by heating. Ultrasonic energy can also used to induce currents within the medium. Likewise, electromagnetic energy can be used to induce currents within the medium when the medium is electrically conductive.
A gas may also be released into the medium to induce currents therein. Preferably, such a gas is sterile and biologically inactive.
In the case that the first container is compressible, the agitation mechanism can operate to compress the first container to induce mixing. For example, the agitation mechanism can include a roller that moves over the first container. Alternatively, the agitation mechanism can compress alternating sections of the first container.
In still another embodiment, the system can operate to circulate the fluid with an agitation pump. The agitation pump and the injection pressurization pump can be the same or different units. Such a system can, for example, include a second container, and the agitation pump can operate to move at least a portion of the medium between the first container and the second container. The medium may be moved between the first container and the second container in an alternating fashion.
The present invention also provides a method of dispensing a multi-component medium. The method includes the step of agitating the medium (for example, as described above) before or during an injection procedure to maintain the components of the medium in a mixed state. As used herein, the phrase xe2x80x9cduring an injection procedurexe2x80x9d refers generally to the time after initial preparation or mixing of the contrast medium through completion of the injection into the patient. The step of agitating the medium can be accomplished as described above.
The present invention, together with its attendant advantages, will be further understood by reference to the following detailed description and the accompanying drawings.